This application proposes the extension to panel design of the theretical model developed in previous phases of the project of biological and social determinants of female sexual behavior in adolescence. The research design replicates insofar as possible the design of the on-going panel study of boys. One hundred white and 100 black 13-year old females will be studied for two years. The primary emphasis is to examine how changes over time in steroid hormones, attractiveness, and social controls determine changes in sexual behavior. The design is organized to explain race and sex differences which have been discovered in previous project work. An important new theoretical element is the specification of biosocial interactions, in which the strength of the relationships between social variables and sexual behavior is hypothesized to be contingent on levels of steroid hormones.